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We report the temperature dependence of the spin–orbit torque (SOT) in the in situ grown Bi2Te3/MnTe heterostructures by molecular beam epitaxy. By appropriately designing the film stack, robust ferromagnetic order with high Curie temperature and strong perpendicular magnetic anisotropy is established in the MnTe layer. Meanwhile, the sharp hetero-interface warrants highly efficient spin current injection from the conductive topological insulator (TI) channel. Accordingly, SOT-driven magnetization switching is observed up to 90 K with the critical current density within the 106 A⋅cm−2 range. More importantly, the temperature-dependent harmonic measurement data can be divided into two categories, namely, the spin Hall effect of the TI bulk states gives rise to a relatively small spin Hall angle in the high-temperature region, whereas the spin-momentum locking nature of the interfacial Dirac fermions leads to the enhancement of the SOT strength once the topological surface states become the dominant conduction channel at deep cryogenic temperatures. Our results offer direct evidence of the underlying mechanism that determines the SOT efficiency and may set up a suitable platform to realize TI-based spin–orbit applications toward room temperature.

We report the growth of InSb/CdTe hetero-epitaxial thin films on the GaAs (111)B substrate using molecular beam epitaxy. The use of (111) orientation enables the fast strain relaxation during the CdTe buffer layer growth, and major crystallographic defects are confined near the CdTe/GaAs interface. Owing to the lattice matching between InSb and CdTe, layer-by-layer 2D growth of InSb is observed from the initial growth stage. Both smooth surface morphology and low defect density of the as-grown InSb/CdTe heterostructures give rise to the enhancement of electron mobility when the InSb layer thickness is reduced below 30 nm as compared to the InSb/GaAs counterparts. The integration of InSb/CdTe highlights the advantage of lattice-matched epitaxial growth and provides a promising approach to design high-quality III–V/II–VI hybrid systems for high-performance device applications.

We report the electrical transport properties of topological Dirac semimetal Cd3As2. Unlike the ordinary Hall resistance with linear slope and the parabolic magnetoresistance (MR) in conventional semiconductors, the linear-band dispersion in this system give rise to a high electron mobility of 3.4 x 10(4) cm/V s and a giant linear MR exceeding 5 x 10(3) % at 2.1 K. More importantly, the large Hall angle-induced phenomena can be captured by applying a generic two-band magneto-transport model on both the Hall and MR data, and the fitting results are consistent over the entire temperature range from 2.1K to 350 K. Furthermore, the large-Hall-angle condition also enables the observation of distinct quantum oscillations with non-trivial band topology of the Cd3As2 sample at low temperatures. Our work provides a general approach to investigate the high-mobility topological Dirac semimetals and their potential applications. Published by AIP Publishing.

We report the observation of the Quantum Hall effect from the topological surface states in both the Dirac electron and Dirac hole regions in a 4 quintuple layer (Bi0.53Sb0.47)2Te3 film grown on GaAs (111)B substrates. The Fermi level is sitting within the enlarged bulk band gap due to the quantum confinement of the ultra-thin film and can be tuned through the Dirac point by gate biases. Furthermore, the Hall resistance Rxy shows even denominator plateaus, which could be fractional Quantum Hall states. This may be due to the hybridization between the top and bottom surface states and suggests the possible way to manipulate the interaction of two surfaces for potential spintronic devices.

The time invariant behaviors of topological insulators are expected to be changed with magnetic doping, which motivate the present study. Here, we show that for Bi2� xCrxSe3 (0.01 � x � 0.3) thin films grown on Si, the non-trivial topological surface state is weakened by the Cr dopants. The band gap of surface is opened and monotonically increased with Cr concentration up to � 100meV at 10K. Meanwhile, the semiconducting behavior is well-maintained in the bulk owing to the reduction of background doping by means of a modified growth strategy and an in situ passivation method. Besides, we also observe the existence of unconventional ferromagnetic ordering below 35K, for which the Curie-Weiss Law and conventional/modified Arrott equations do not apply. These observations may further help us investigate extraordinary magneto-electric effect in topological insulators, and the result will also pave the way for realizing the quantized anomalous Hall effect. V C 2012 American Institute of Physics .[ http://dx.doi.org/10.1063/1.4754452]

In this paper, we report the epitaxial growth of Bi2Se3 thin films on Si (111) substrate, using molecular beam epitaxy (MBE). We show that the as-grown samples have good crystalline quality, and their surfaces exhibit terracelike quintuple layers. Angel-resolved photoemission experiments demonstrate single-Dirac-conelike surface states. These results combined with the temperature- and thickness-dependent magneto-transport measurements, suggest the presence of a shallow impurity band. Below a critical temperature of ∼100K, the surface states of a 7 nm thick film contribute up to 50% of the total conduction.